The present invention relates, in general, to the field of magnetoresistive ("MR") spin valve ("SV") devices and methods for fabricating the same. More particularly, the present invention relates to a shaped magnetoresistive spin valve device design and process for manufacturing the same for use as a magnetic transducer or "head" for reading data signals encoded on a magnetic mass storage medium.
Magnetoresistive devices or heads exhibiting so called giant magnetoresistance ("GMR") are of current technological interest in an attempt to achieve high areal density recording in magnetic computer mass storage disk drives and tapes. The GMR effect was first described by M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen Van Dau, F. Petroff, P. Etienne, G. Creuzet, A. Friederich and J. Chazelas in Phys. Rev. Lett. 61, 2472 (1988). Typically, the magnitude of the magnetoresistive ratio (".DELTA.R/R") for GMR materials exceeds that of anisotropic magnetoresistive ("AMR") materials which are currently in use as magnetic read-transducers.
The spin valve effect is one known way to utilize GMR as described by B. Dieny, V. S. Speriosu, S. S. P. Parkin, B. A. Gurney, D. R. Wilhoit and D. Mauri, Phys. Rev. B 43, 1297 (1991). A typical spin valve MR device comprises two thin ferromagnetic layers separated by a nonmagnetic metal spacer. The magnetization of one ferromagnetic layer is allowed to move freely, whereas the other one is pinned by an adjacent antiferromagnetic or permanent magnetic layer. Essential to the operation of any type of GMR structure is the fact that the MR response is a function of the angle between two magnetization vectors corresponding to the sensing field.
A number of patents have previously described various device implementations utilizing the spin valve effect. See for example U.S. Pat. No. 5,159,513 to Dieny et al. for "Magnetoresistive Sensor Based on the Spin Valve Effect" issued Oct. 27, 1992; U.S. Pat. No. 5,206,590 to Dieny et al. for "Magnetoresistive Sensor Based on the Spin Valve Effect" issued Apr. 27, 1993; U.S. Pat. No. 5,287,238 to Baumgart et al. for "Dual Spin Valve Magnetoresistive Sensor" issued Feb. 15, 1994; and U.S. Pat. No. 5,301,079 to Cain et al. for "Current Biased Magnetoresistive Spin Valve Sensor" issued Apr. 5, 1994, all assigned to International Business Machines Corporation.
The stacked, orthogonal structures of the various device implementations therein described locate a lower ferromagnetic layer (on which the freely rotating magnetization vector resides) above the substrate but below the upper ferromagnetic layer having its magnetization vector pinned by an adjacent antiferromagnetic pinning layer. Although the first listed patent indicates that the structure might be inverted, wherein the latter pinned ferromagnetic layer underlies the former freely rotating ferromagnetic layer, it nevertheless appears that it would be difficult to achieve a sufficiently high current density with the design described to provide an enhanced sensor output signal inasmuch as high resistivity materials (such as the capping layer for example) are interposed between the current leads and the top-most ferromagnetic layer. Moreover, whether inverted or not, the read track width cannot be accurately or reproducibly defined without difficulty due to the fact that both the current leads and the contiguous permanent magnet regions may effect it and precise track width definition through photolithographic processing of the relatively thick conductive layer is problematic at best. Further, precise control of the domain stabilization layer is also extremely difficult due to the relative thinness of the layers involved (on the order of less than 100 .ANG.) and the fact that the total magnetic moment ("M.sub.r .cndot.t") which determines the strength of the stabilization is limited by the thickness of the contiguous permanent magnet layer. Utilizing a thicker permanent magnet layer to compensate for these shortcomings could have the unintended consequence of altering the magnetization of the pinned ferromagnetic layer.